1. Field of the Invention
This invention relates to valves used to seal and to control the flow of gas from gas cylinders. In particular, the invention relates to such valves in which the surface area of the valve exposed to gas discharged from the gas cylinder is minimized.
2. Background of Information
Many types of gases are transported in, stored in and discharged from gas cylinders. Commonly, the valves used on high pressure gas cylinders have a set of diaphragms which isolate the valve member from an actuating stem. A spring within the valve chamber biases the valve member to an open position. The stem is actuated by a hand wheel or an automatic actuator such as a pneumatic actuator. Examples of such cylinder valves are described in U.S. Pat. No. 4,706,929 and 4,776,562. In such a valve, the valve member, the diaphragms and the actuating stem bear against but are not fixed to each other, as the spring pushes the parts to the valve open position and the stem pushes them to the closed position.
In some applications, the gas dispensed from the gas cylinder must remain free of impurities. This is especially true in the semiconductor industry where any impurities in the gas can adversely affect the electrical properties of the device and can greatly decrease the manufacturing yield.
It has been found that the spring which is in the wetted area of the above described gas cylinder valves generates particulates which are discharged with the gas or which accumulate in the wetted areas of the valve and are discharged in bursts.
To eliminate the particulates generated by the spring located in the wetted area, a valve has been offered which eliminates the spring entirely. In that valve, the actuating stem is connected to a pneumatic actuator by a tongue and groove connection. Without the spring in the valve chamber, the valve member must be physically pulled to the open position. This requires connecting the valve member, diaphragms and actuating stem together so that when the valve stem is pulled, the diaphragms and valve member follow. In the above described valve, the valve member has an integral threaded stud which extends through central apertures in the diaphragms and the parts are fused together by a weld extending around the periphery of the threaded stud. The valve stem screws down onto the threaded stud to connect the valve stem to the valve member. Such a valve requires an exemption for use with highly toxic gases such as those used in the semiconductor industry as the Department of Transportation (DOT) prohibits the use of perforated diaphragms in such applications.
There is a need for an improved cylinder valve which is non-particulating.
More particularly, there is a need for a cylinder valve in which the wetted area within the valve is minimized.
There is a related need for such a cylinder valve in which the usual spring is removed from the wetted area, but preferably still provided in the valve to bias the valve to the open position.
There is a further need for such a valve without a spring in the wetted area in which the valve member, diaphragms and valve stem are fused together so that that the valve member may be pulled open, but in which the diaphragms are non-perforated.
There is an additional need for such a cylinder valve in which the weld by which the parts are fused together is isolated from the stresses developed in the diaphragms as they flex during operation of the cylinder valve so that the cycle life of the diaphragms can be maximized.